- Author
- Nguyen, T.
- Title
- Thermal-Wave Microscopy in Corrosion Studies.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Journal
- Materials Characterization, Vol. 28, 291-309, 1992
- Keywords
- corrosion | microscopy | steels | humidity | water | coatings | quantitative analysis | thermal conductivity
- Abstract
- All forms of metallic corrosion cost the United States 4.3% of its gross national product, about $175 billion per year at the present value. Corrosion costs may be reduced by understanding how and why corrosion occurs and then by changing the conditions that promote it. The most commonly used microscopical techniques to detect and characterize early corrosion of metals have been scanning electron and light microscopies. A body of information has been accumulated in the past several years demonstrating that a new technique, thermal-wave microscopy (TWM), has considerable promise as a nondestructive tool for obtaining information on a micrometer scale about the surface and near-surface features of transparent and opaque materials. The technique, which is sensitive to minor variations in the thermal conductivity of materials (such as those caused by grain boundaries, deformed structures, and defects), can potentially image the microstructure and corrosion products of metal with and without a coating. We have applied TWM using an electron beam as the thermal excitation source [electron thermal-wave microscopy (ETWM)] to study corrosion of bare steel and also of steel under organic protective coatings. This article presents the results of these studies. Because the images resulting from TWM appear dramatically different from those obtained by light or scanning electron microscopy, and because the use of TWM has been limited primarily to the semiconductor industry, a brief summary of the principle and its current applications in material science is presented in the following section.